Kids get addicted to cigarettes a lot quicker than we thought. Mayo Clinic researchers report this month that children who have smoked only a few cigarettes experience the same symptoms of nicotine addiction as adults who smoke heavily.

The researchers followed more than 600 12- and 13-year-olds from seven schools in central Massachusetts for a four year period. Even kids who only smoked a few cigarettes a week became strongly addicted. "This is particularly disturbing," adds lead study author Dr. Joseph DiFranza, "given that each day, over 4,800 teens smoke their first cigarette. That's 1.7 million children annually."

The chemical nature of nicotine addiction is a tragedy but not a mystery. Scientists understand nicotine addiction quite well. The key experiment that led to our understanding was a simple one: Investigators introduced radioactively-labelled nicotine into the brain and looked to see where it went. They found that individual nicotine molecules attached themselves to a previously unknown protein on the surface of brain nerve cells!

These so-called "nicotine receptors" usually bind a natural brain chemical, acetylcholine. It was just an accident of nature that nicotine, an obscure chemical from a tobacco plant, was also able to bind to them. What then is the normal function of the nicotine receptors?

Each activity in the brain involves constant communication between nerve cells. One nerve cell communicates with another by throwing a chemical at it. The target cells have on their surface receptor proteins, each with a shape that "fits" that chemical signal and no other. Like playing catch, communicating nerve cells lob these signal chemicals back and forth.

Different brain cells carrying out different activities often use different chemical signals. The signals include chemicals such as acetylcholine, dopamine, serotonin, glutamate, glycine, and a host of others.

With all this signalling going on, the brain cannot function effectively without a way to coordinate its many activities -- to adjust a particular activity "UP" or "DOWN" relative to others. The brain does this in a direct and logical way, by adjusting the sensitivities of each of its many different kinds of receptors to their chemical signals.

The tool it uses to do this is a central coordinating receptor -- the very one to which nicotine binds. The role of this receptor is to "fine tune" the sensitivity of a wide variety of other brain receptors to their chemical signals, adjusting particular kinds of receptors up or down to slow some activities, speed others, and in this way to achieve overall coordination of the brain's activities.

So how does nicotine cause chemical addiction? When neurobiologists compare the brain nerve cells of smokers to those of nonsmokers, they find that nicotine binds this coordinating receptor, stimulating it. By overriding the normal system used by the brain to coordinate its many activities, nicotine alters the pattern of release by nerve cells of many neurotransmitters, including acetylcholine, dopamine, serotonin, and many others -- like turning up the setting on a TV remote that controls many television sets. As a result, changes in level of activity occur in a wide variety of nerve pathways within the brain. These changes are responsible for the profound effect smoking has on the brain's activities.

Addiction occurs because the nervous system responds piecemeal to nicotine's fiddling with its central control. The brain attempts to "turn the volume back down" by readjusting the sensitivities of each kind of receptor individually, eventually restoring an appropriate balance of activity. Unfortunately, in many children these readjustments apparently occur after only a few cigarettes.

Now what happens if you stop smoking? Everything is out of whack! The newly coordinated system requires nicotine to achieve an appropriate balance of nerve pathway activities. You are addicted to nicotine.

So what do you do, if you are addicted to smoking cigarettes and you want to stop? The CDC reported in July that 8 million people tried to quit smoking in 1998, the latest data available. About half the people attempting to quit smoking use patches containing nicotine to help them, and another quarter chew nicotine gum. Providing nicotine removes the craving for cigarettes -- so long as you keep using the patch or gum. Actually, using nicotine patches or gum simply substitutes one (admittedly less dangerous) nicotine source for another. You are still addicted.

If you are going to quit smoking, there is no way to avoid the necessity of eliminating the drug to which you are addicted, nicotine. Hard as it is to hear the bad news, there is no easy way out. The only way to quit is to quit. Every teen should consider carefully the take-home lesson, which is that addiction to nicotine is not a matter of will power, but chemistry. "These kids will take about 20 years on average to break this addiction," DiFranza warns. How much easier not to smoke the first cigarette.